Phases of Clinical Trials for Drugs

Clinical trials for drugs assess the safety and efficacy of new pharmaceutical compounds. Trials typically consist of several phases, each serving a specific purpose in drug development.

Trial Participants	Trial Endpoints	Regulatory Pathways	Post-Market Surveillance
Patients with the target medical condition and, sometimes in early phases, healthy volunteers.	Typically related to the disease or condition such as symptom improvement, disease progression, or survival rates.	In the United States, clinical trials for drugs are governed by agencies like the Food and Drug Administration (F.D.A.).	Monitoring of safety and efficacy in real-world settings.

Trial Participants

Trial Endpoints

Regulatory Pathways

Post-Market Surveillance

Patients with the target medical condition and, sometimes in early phases, healthy volunteers.

Typically related to the disease or condition such as symptom improvement, disease progression, or survival rates.

In the United States, clinical trials for drugs are governed by agencies like the Food and Drug Administration (F.D.A.).

Monitoring of safety and efficacy in real-world settings.

Phases are designed to assess drug safety, dosage & efficacy

Can the drug in question treat, cure, or prevent a specific medical condition (i.e., disease state)? This question is addressed through a well-defined, four-phase process that sometimes includes an exploratory phase. Keep in mind that you’ll often see clinical trial phases use Roman numerals; for example: IV rather than four.

Phase I: Safety & dosage

Researchers determine the optimal dosage range, methods of administration, and pharmacokinetics (i.e., how a drug is affected as it moves into, through, and out of people).

Objectives: Assess drug safety, determine a safe dosage range, and identify potential side effects.

Participants: Small number of healthy volunteers or patients (20-80 people).

Duration: Several months.

Phase II: Efficacy & side effects

Researchers gather more information about a drug’s effectiveness for treating the targeted condition as well as any adverse reactions among the hundreds of participating patients.

Objectives: Further evaluate safety and start to assess effectiveness.

Participants: Larger group of patients (30-300 people) who have the condition the drug is meant to treat.

Duration: Up to two years.

Phase III: Confirmation

Researchers aim to confirm drug efficacy, identify side effects, and contrast with commonly used treatments in larger groups or a placebo; this helps regulatory authorities make approval decisions based on substantial data on safety and effectiveness.

Objectives: Confirm effectiveness, monitor side effects, compare to standard treatments, and collect information that allows for safe use.

Participants: From several hundred to several thousand patients.

Duration: One to four years.

Phase IV: Surveillance

Post-marketing surveillance occurs after a drug has been approved and is available on the market. Such ongoing monitoring of drug safety and effectiveness takes place in a larger patient population. New side effects or long-term effects may be discovered during this phase, leading to updates in usage guidelines or even withdrawal from the market.

Objective: Gather more information on risks, benefits, and optimal use.

Participants: Various, post-approval.

Duration: Varies, potentially ongoing.

During all phases, data are collected & participants closely monitored

Study results are submitted to regulatory agencies, such as the F.D.A. in the United States, for review and approval. If the drug successfully completes all phases and meets regulatory standards for safety and efficacy, it can be granted market approval and made publicly available. This differs from the different phases of diagnostic trials.